The primary objective of this project is to develop a method for high-resolution 3-dimensional (3D) diffusion-weighted MRI (DWI) of the brain. Over the last several years, DWI has been established as a very useful technique for clinical and scientific neuroimaging. Because the diffusion properties of water in living tissue are extremely sensitive to the microscopic environment of the tissue (e.g. cellular architecture, membrane integrity, temperature) DWI can be used to non-invasively investigate the microstructural details of tissue in vivo. For DWI in the brain, it would be ideal to obtain images with high spatial resolution in three dimensions and to employ techniques that are insensitive to magnetic field inhomogeneities. Radial fast spin-echo (RAD-FSE) MRI methods have been shown to be effective in reducing sensitivity to motion in DWI and enable diffusion-weighted images to be obtained with high spatial resolution in 2-dimensions. These methods are insensitive to bulk motion and do not have the artifacts due to magnetic field inhomogeneities. Within this project, RAD-FSE methods will be extended to enable DWI to be carried out at high spatial resolution in three dimensions (3D) for whole brain DWI. The increased spatial resolution will enhance the usefulness of DWI as a tool for neurological investigations of the human brain. This is particularly true in diffusion tensor imaging (DTI) where the details of the anisotropy of water motion in the brain can be more accurately determined. The insensitivity of the method to magnetic field inhomogeneities will be particularly useful for neuroimaging at higher magnetic field strengths, e.g. 3.0T, where susceptibility artifacts are more problematic.